There are NO drives by default.The OS and the other things all come under one directory-ROOT represented by "/ "

Here is how the Linux Directory Structure is-

The /Home is similar to your My Documents+My Computer

Well,Though the structure is not Drive-based,like windows,you can create partitions(drives) similar to windows(But they wont be named C: or D:...You may label them as seen in the screenshot below or they will be named New Volume1/2/3etc).They are treated as an external media(somewhat like a usb).In linux,anything other than the what is under "/ " by default is an outsider(and so are the partitions/drives).

Here is how the drives will look if you hve them-

The Devices part you see in the upper left corner are the drives(the Eject arrow shows how they are treated or considered as external devices).